CBSE Class 11-science Answered

The enthalpy of a system is defined as:

so

dH(S,p) = TdS + Vdp

where

H is the enthalpy of the system

U is the internal energy of the system

p is the pressure at the boundary of the system and its environment

V is the volume of the system.

The standard enthalpy of formation is used in thermochemistry to find the standard enthalpy change of reaction. This is done by subtracting the sum of the standard enthalpies of formation of the reactants (each being multiplied by its respective stoichiometric coefficient, ?) from the sum of the standard enthalpies of formation of the products (each also multiplied by its respective stoichiometric coefficient), as shown in the equation below:

?H° = ?(? × ?H_f°) (products) - ?(? × ?H_f°) (reactants)